Field of the Disclosure
The present disclosure relates to a multiple-input/multiple-output (MIMO) antenna for a vehicle, and more particularly to a multi-band MIMO antenna for a vehicle, which is capable of achieving an improvement in isolation and an enhancement in bandwidth, using a coupling stub.
Discussion of the Related Art
Recently developed wireless communication technologies realize the provision of voice communication services and high-quality multimedia services through a portable terminal for mobile communication and, as such, combination thereof with a next-generation wireless communication service such as long term evolution (LTE) is being highlighted.
Generally, communication systems based on voice communication services mainly use a single-input/single-output (SISO) system in which only a single antenna mainly having narrow-band channel characteristics is used within a limited frequency band. However, there are many difficulties in transmitting big data over a narrow-band channel, using the SISO system in which a single antenna is used. For this reason, further developed technology is needed.
To this end, next-generation wireless transmission technology, namely, multiple-input/multiple-output (MIMO) technology, in which a plurality of antennas is used in such a manner that each antenna operates independently, to achieve data transmission and reception at higher data transmission and reception rates while reducing possibility of generation of errors, is needed.
Such a MIMO system uses multiple antennas at transmission and reception stages thereof and, as such, realizes high-speed data transmission without an increase in frequencies allocated to the overall system. Accordingly, the MIMO system provides an advantage in that limited frequency resources can be efficiently used. By virtue of such an advantage, the MIMO system is applied to high-speed wireless packet data communication such as LTE or worldwide interoperability for microwave access (WiMAX).
However, the multiple antennas used in the MIMO system, namely, the MIMO antennas, should overcome degradation of transmission and reception performance caused by electromagnetic mutual coupling or insufficient isolation between adjacent antennas. In order to solve such problems, a method of spacing the adjacent antennas apart from each other by a distance of λ/2 or more (λ being the wavelength of radio waves radiated by the antennas) may be proposed.
In a small-size antenna system, however, the above-mentioned problem cannot be solved by the method of spacing the adjacent antennas because the small-size antenna system has a limited antenna installation space.
Meanwhile, in accordance with development of communication technologies for vehicles, a vehicle antenna, which supports, in a vehicle, diverse wireless communication services associated not only with existing broadcast radio frequency signals such AM and FM signals, but also with digital multimedia broadcasting (DMB), global positioning system (GPS), and mobile communication, is being highlighted.
Such a vehicle antenna includes a glass antenna having a unified configuration of AM and FM antennas, and a shark fin antenna designed to enable services associated with, for example, GPS and Terrestrial-DMB (T-DMB). The antennas are installed inside and outside the vehicle, respectively.
In a conventional shark fin antenna, however, there may be problems in that, due to exposure thereof to the outside of the vehicle, the antenna may degrade the appearance of the vehicle, and may be damaged by external environments and external pressure. Furthermore, there is a difficulty in installing the antenna. In addition, during high-speed travel of the vehicle, noise may be generated as the antenna is struck by the wind.
Therefore, in the technical field to which the present invention pertains, development of an antenna capable of supporting a MIMO system to be built in a vehicle while having wide-band characteristics, and securing desired isolation and desired correlation is greatly required.